Roofing materials, such as roofing shingles, are made from a wide variety of materials, including metal, slate, concrete, plastic, asphalt, etc.
The advantages of metal roofs are that they are aesthetically pleasing, durable, long lasting, lightweight, ecologically sound, fire retardant, and energy efficient. The disadvantages of metal roofs are that they are expensive, require installation by a professional trained in metal roofing installation, and can be damaged or dented by outdoor elements, such as hail. Tegola (Pasiano, Italy) manufactures a copper foil shingle which is an asphalt strip shingle that has a copper foil over the exposed portion of the shingle. The copper foil-asphalt strip shingle is easier to install than conventional metal shingles.
Slate roofs have the advantages of long life, fire resistance, high strength, relatively low maintenance, and an aesthetically distinctive appearance. Slate roofs, however, are heavy and expensive. Further, slate exists in limited color choices, can be easily damaged (particularly during maintenance due to walking on the roof), and relies on underlayment which usually fails before the slate.
Asphalt roofing materials have the advantages of good performance in extreme temperatures and areas where wind, water and ice are of concern. In addition, asphalt roofing materials offer enhanced efficiency in that they can be produced in high volume and can be easily installed, resulting in lower costs and improved overall value. Furthermore, asphalt roofs can be made with colored asphalt to produce a colored roofing surface tailored to desired color, reflectance, and emittance. However, many asphalt roofing materials do not have the same aesthetic qualities as metal and slate roofs and most do not have the equivalent life span. Additionally, colored asphalt roofing materials can be very expensive.
Pigment-coated mineral rocks are commonly used as color granules in roofing applications to increase the aesthetic and protective functions of asphalt shingles. Roofing granules typically are made of crushed and screened mineral materials that, subsequent to crushing and screening, can be coated with a binder containing one or more coloring pigments such as suitable metal oxides. The binder can be a soluble alkaline silicate that is subsequently insolubilized by heat or by chemical reaction, resulting in an insoluble colored coating on the mineral particles. Preparation of colored, coated roofing granules is disclosed for example, in U.S. Pat. No. 2,981,636 of Lodge et al. The granules are then employed to provide a protective layer on asphaltic roofing materials such as shingles.
Pigments for roofing granules have usually been selected to provide shingles having an attractive appearance, with little thought to the thermal stresses encountered on shingled roofs. However, depending on location and climate, shingled roofs can experience very challenging environmental conditions, which tend to reduce the effective service life of such roofs. One such environmental stress is the elevated temperature experienced by roofing shingles under sunny, summer conditions, especially roofing shingles coated with dark colored roofing granules.
Asphalt shingles coated with conventional roofing granules are known to have low solar heat reflectance, and hence will absorb solar heat especially through the near infrared range (700 nm-2500 nm) of the solar spectrum. This heat absorption characteristic is increased as the granules covering the surface become darker in color. For example, white colored asphalt shingles can have solar reflectance in the range of 25-35%, whereas dark colored asphalt shingles may have solar reflectance of only 5-15%. There is a continuing need for roofing materials that exhibit excellent reflectance, as well as emittance, characteristics while being aesthetically pleasing. It has been proposed to replace asphalt shingles with shingles coated in metal flakes. However, such shingles, while reflective, generally do not have satisfactory emittance characteristics and may not be considered aesthetically pleasing for certain applications.
U.S. Pat. No. 2,133,988 describes a method of increasing shingle durability by using very fine aluminum flakes on the shingle surface between the larger mineral surfacing rock to block ultraviolet degradation of the asphalt coating and to lower the temperature of the shingle, thereby promoting asphalt stability and preventing blistering. U.S. Pat. No. 2,332,219 describes mixing the aluminum flakes with other materials to reduce dust, increase asphalt compatibility for reflowing the aluminum to the surface, and aid in adhering the aluminum flakes. The aluminum flakes may be used as the sole shingle covering or may be blended with mineral surfacing. The aluminum flakes may be adhered to other mineral rock granules and aluminum dross may be used as a granule or surface granule in whole or in part. The size of the flakes ranges between 150 and 350 mesh.
U.S. Pat. No. 4,617,198 discloses a metal chip application equipment for low slope applications. A water bath is used to cool a modified cap sheet and the chips are projected or flung onto the sheet. Chip materials include aluminum, magnesium and tin. The chips are rectangular chips having a size ranging from 10 to 200 mils on a side, preferably 60 to 80 mils on a side, by 1 to 2 mils thick. The patent also discloses that chips having a larger size than 200 mils on a side are not suitable due to their inability to withstand wind gusts when the cap sheet having the metal chips is applied on a roof.
Accordingly, there exists a need for a roofing material with improved durability and aesthetic qualities. There is also a need for a roofing material which has an appearance of a metal or slate shingle but which can be colored to have desired reflectance and emittance levels.